1. Field of the Invention
The present invention generally relates to a video coding method. More particularly, the present invention relates to a video coding method for improving the compression rate of motion vector information.
2. Description of the Related Art
The standard H.264/AVC that has recently been completed promises excellent rate-distortion performance, using a block coding scheme like other conventional video compression standards. H.264/AVC divides a coding unit, macro block into a plurality of subunits of a variable block size and performs motion compensation by predicting the motion vectors of the divided blocks.
Motion vectors of a macro block being a coding unit are predicted and compensated in an inter-mode, SKIP, P16×16, P16×8, P8×16, or P8×8 (P8×8, P8×4, P4×8, or P4×4). With this variable block size-motion compensation technique, a maximum of 16 motion vectors are generated for a single macro block in H.264/AVC. This means that a large number of bits are required for encoding motion vector information. The size of subunits that are divided from a macro block is decided for variable block size-motion prediction, comprehensively considering positive effects that subunit-based fine motion compensation brings and negative effects from the bit overhead of transmitting additional information about a plurality of motion vectors and coding unit segmentation information indicating how a given coding unit is segmented into subunits, each being a motion compensation unit.
In the case of variable block size-segmentation, as a coding unit is divided into more subunits, less residual data is generated after motion compensation. However, since motion vectors are created according to the number of the divided subunits, the number of motion vectors increases. Despite the decrease of residual data to be encoded, the increase of motion vectors in number leads to an increase in the number of required bits. Consequently, the effects of motion compensation on a subunit basis are not successfully exerted.